JP2004109020A - P-channel field effect transistor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a p-channel field effect transistor having a high threshold voltage by ozone processing, and having an excellent characteristic. <P>SOLUTION: A liquid electrolyte is used as a gate 8, and a hydrogen terminal surface is partially oxidized by the ozone processing 2, to thereby acquire the p-channel field effect transistor having as a channel, a diamond surface wherein a hydrogen terminal and an oxygen terminal are intermingled. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a p-channel field-effect transistor using a liquid electrolyte as a gate and using a diamond surface as a channel in which hydrogen termination and oxygen termination or hydrogen termination and amino termination are mixed.
[0002]
[Prior art]
Conventionally, an ion-sensitive FET (ISFET) based on a commercially available SiMOSFET has a structure in which an Si oxide film is covered with a Si nitride film in order to prevent malfunction due to intrusion of ions into an oxide film or an oxide film / Si interface. Has become. Since the surface of the Si nitride film covering the Si oxide film is a sensitive portion, the sensitive portion is separated from the oxide film / Si interface, and a current change corresponding to a potential change on the surface is small, making it difficult to increase sensitivity. is there.
[0003]
To cope with this, a film-forming technology is used to increase the density of the silicon nitride film and alumina film as the sensitive film and protective film, use laser ablation, etc., and reduce the film thickness to increase the sensitivity. .
[0004]
[Non-patent document 1]
H. Kawarada, Surface Science Reports 26 (1996) 205
[Non-patent document 2]
G. FIG. W. Swain, Advanced Materials, 6, (1994) 388.
[Non-Patent Document 3]
Akira Fujishima; Chemistry and Industry 51, (1998) 207
[0005]
[Problems to be solved by the invention]
The inventors of the present application produced a p-channel field-effect transistor using the ozone-treated surface, in which the channel resistance increased. Furthermore, it has been found that the threshold voltage moves in the negative direction. At that time, it was revealed by photoelectron spectroscopy (XPS) that the diamond surface as a channel was oxygen-terminated.
[0006]
And as such a field effect transistor,
(1) Since the transistor operation is excessively affected by various ions in the liquid electrolyte, a field effect transistor having a surface channel that is not ion-sensitive is required as a transistor for determining a reference potential.
[0007]
(2) There is a need for a transistor formation technology that can directly fix any organic molecule or biomolecule to the sensitive channel.
[0008]
As techniques in such a field, there are the above-mentioned non-patent documents 1 to 3.
[0009]
ISFETs (ion-sensitive field-effect transistors) have been actively studied due to their advantages of integration and miniaturization, and those using Si have already been marketed. Since diamond is physically and chemically stable, it is expected to be a biocompatible biosensor in the future.
[0010]
In addition, boron-doped diamond exhibits p-type semiconductor conductivity. Undoped diamond whose surface is terminated with hydrogen also has a p-type conductive layer on the surface. This hydrogen-terminated surface conductive layer shows a high surface carrier density (10 ¹³ / cm ² ) even at room temperature, and shows almost no temperature dependence. Furthermore, most carriers are present in a shallow region from the surface (〜１０10 nm). Since such a structure is advantageous for the operation of the FET, the inventors of the present application are studying ISFETs using undoped diamond that has been subjected to hydrogen termination.
[0011]
Further, since the hydrogen-terminated structure is obtained as-grown by the microwave plasma CVD method for synthesizing diamond, it is possible to obtain p-type semiconductor conductivity more easily than boron doping. Boron-doped diamond electrodes have a wide potential window, are less affected by dissolved oxygen, and have a small background current, and electrode research has progressed in a wide range. The present inventors have already confirmed that undoped hydrogen-terminated diamond has a wide potential window as in the case of the boron-doped diamond electrode, and have developed the diamond ISFET for the first time in the world using this.
[0012]
As described above, the inventors of the present application have further studied the structure of the channel. As a result, the present invention aims to provide a p-channel field-effect transistor having a high threshold voltage by ozone treatment and excellent characteristics. .
[0013]
[Means for Solving the Problems]
The present invention, in order to achieve the above object,
[1] In a p-channel field-effect transistor, a liquid electrolyte is used as a gate, and a hydrogen-terminated surface is partially oxidized by ozone treatment so that a diamond surface in which hydrogen-terminated and oxygen-terminated are mixed is used as a channel. is there.
[0014]
[2] The p-channel field-effect transistor according to [1], wherein the threshold voltage can be shifted in the negative direction by increasing the oxygen coverage.
[0015]
[3] In the p-channel field effect transistor according to the above [1], a change in pH1 to pH14 of the liquid electrolyte and an increase in negative ions such as positive ions such as alkali ions and negative ions such as halogen ions from 10 ⁻¹ to 10 ⁻⁶ mol / liter. On the other hand, the threshold voltage does not change within a range of ± 0.1 V.
[0016]
[4] In a p-channel field effect transistor, a liquid electrolyte is used as a gate, a hydrogen-terminated surface is aminated by a mixed plasma of hydrogen and nitrogen, and a diamond surface having both hydrogen-terminated and amino-terminated is used as a channel. It is.
[0017]
[5] The p-channel field effect transistor according to the above [4], wherein a divalent carboxylic acid is allowed to act on the amino terminus via a peptide bond to perform carboxylation.
[0018]
[6] The p-channel field-effect transistor according to the above [5], wherein the amino terminus is carboxylated by a peptide bond, and the DNA is further immobilized by a peptide bond.
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the details from the conventional research to the present invention will be described in detail.
[0020]
Diamond is a material that can meet the demands of application to various devices because of its wide band gap, high mobility, high thermal conductivity and wide potential window. A device using diamond has been manufactured for the first time [Ref. Kawarada, M .; Aoki and M.S. Ito, Appl. Phys. Lett. 65, 1563 (1994)], and diamond is a high-power high-frequency device [Ref. Gluche, A .; Aleksov, A .; Vescan, W.C. Ebert and E.A. Kohn, IEEE Electron Device Lett. Vol. 18, No. 11 (1997), Reference [3]: H. et al. Taniuchi, H .; Umezawa, T .; Arima, M .; Tachiki and H.S. Kawarada, IEEE Electron Device Lett. Vol. 22, No. 8 (2001)], and biosensors.
[0021]
Due to the hydrogen termination without doping, a p-type surface conductive layer of diamond having a hydrogen termination structure having a high surface carrier density (１３10 ¹³ cm ⁻² ) was obtained. This was stable even at a temperature range of 150K to 400K [Ref. Hayashi, S .; Yamanaka, H .; Okushi and K.K. Kajimura, Appl. Phys. Lett. 68, 376 (1996)].
[0022]
The highly conductive layer can be removed by chemical cleaning, annealing covering the periphery with oxygen, or oxygen plasma treatment [Ref. Kawarada, Surface Science Reports 26, 205 (1996)]. The removal of the highly conductive layer is caused by the substitution in which hydrogen atoms are chemically absorbed by oxygen atoms on the surface.
[0023]
Both an enhancement mode (normally off) field effect transistor and a depletion mode (normally on) field effect transistor can be realized by a gate metal on the surface of diamond having a hydrogen termination structure (the above-mentioned reference [5]). Here, an attempt was made to control the threshold voltage only with the gate metal without sacrificing the function of the threshold voltage as a diamond field effect transistor. However, control of the threshold voltage (Vth) of the diamond conductive layer has not been realized so far.
[0024]
Furthermore, by assisting microwave plasma by a vapor phase growth method, a polycrystalline diamond film was synthesized on a silicon substrate, and a liquid electrolyte gate diamond field effect transistor was formed thereon [Ref [6]: H. Kawarada, Y .; Araki, T .; Sakai, T .; Ogawa and H.S. Umezawa, Phys. Status Solidi A185, 79 (2001)].
[0025]
Hereinafter, embodiments of the present invention will be described in detail.
[0026]
FIG. 1 is a schematic view of an ozone (O ₃ ) -treated field effect transistor showing an embodiment of the present invention, and FIG. 2 is a schematic view of the ozone (O ₃ ) -treated channel portion (dotted line in FIG. 1). FIG. 3 is a characteristic diagram of the threshold voltage [V] with respect to the KCl solution concentration [M] as the gate.
[0027]
1 and 2, 1 is a high-resistance surface channel, 2 is an ozone (O ₃ ) treatment, 3 is a p-type surface conductive layer, 4 is a source electrode, 5 is a drain electrode, and 6 is an epoxy covering the source electrode 4. A resin, 7 is an epoxy resin covering the drain electrode 5, 8 is a gate made of KCl as a liquid electrolyte, 9 is a reference electrode (Ag / AgCl), and 10 is an undoped polycrystalline diamond layer.
[0028]
In this example, as shown in FIG. 1, diamond field effect transistors (FETs) having a high-resistance surface channel 1 were manufactured by ozone (O ₃ ) treatment 2. By this ozone treatment 2, the surface conductive layer of diamond was gradually lost. As shown in FIG. 3, after the ozone treatment c for 60 minutes, the sheet resistance became 20 to 30 times that of the d surface not subjected to the ozone treatment, causing a shift of the threshold voltage (Vth) of 0.44 V. The absolute value of the threshold voltage increased as the ozone treatment time increased. Therefore, it was found that the threshold voltage can be controlled by the ozone treatment. In addition, a in FIG. 3 shows 20 minutes after the ozone treatment, and b shows 40 minutes after the ozone treatment.
[0029]
The drain electrode 5 and the source electrode 4 are covered with epoxy resins 6 and 7 to protect them from the liquid electrolyte 8 and the ozone treatment (O ₃ ) 2. The channel region of the diamond surface not covered with the epoxy resins 6 and 7 is in direct contact with the liquid electrolyte 8 and the oxide ozone.
[0030]
A reference electrode (Ag / AgCl) 9 was used as a gate electrode. All devices were fabricated in p-type surface conductive layer 3 in enhancement mode, with a channel length of 500 μm and a width of 10 mm.
[0031]
It has been reported that diamond having a hydrogen terminal structure exhibits sensitivity to chloride ions (Cl ⁻ ) [Ref. Sakai, H .; Kanazawa, Y .; Araki, H .; Umezawa, M .; Tachiki and H.S. Kawarada, Jpn. J. Appl. Phys. 48, 2595 (2002)].
[0032]
Therefore, the surface change can be easily evaluated by using chloride ions. Therefore, a potassium chloride (KCl) solution having a high concentration (10 ⁻² mol / liter) is used as a liquid electrolyte, and the FET has a potential window. Biased into a diamond of about 3 V [Ref. Tenne, K .; Patel, K .; Hashimoto and A. Fujishima, J. et al. Electroanal. Chem 347, 409 (1993)].
[0033]
After the 60-minute ozone treatment c (see FIG. 3), the sheet resistance was 20 to 30 times higher than the surface of d (see FIG. 3) that was not subjected to ozone treatment. FIGS. 4A and 4B show I _DS (drain-source current) -V _DS (drain-source voltage) characteristics before and after the ozone treatment c (see FIG. 3) for 60 minutes.
[0034]
This I _DS -V _DS characteristic qualitatively matches that of conventional MISFETs. Here, by controlling the gate voltage _{(V GS),} the drain current attempts to maintain at _V DS = per -0.4V in -80μA. After 60 minutes of ozone treatment c (see FIG. 3), V _GS shifted from −0.7 V (see FIG. 4 (a)) to −1.1 V (see FIG. 4 (b)). Since the channel has become highly resistive due to the ozone treatment, the absolute value of the gate voltage (V _GS ) increases to maintain the drain current. The transconductance (g _m ) after the ozone treatment was the same as before the treatment. Carriers on the drain and source sides migrated to the channel to create a surface conductive layer due to the large negative channel bias.
[0035]
The energy band of the hydrogen-terminated diamond is bent upward to form an accumulation layer as shown in FIG. 5 (a). Several models [Ref. [9]: S. G. FIG. Ri, T .; Mizumasa, Y .; Akiba, Y .; Hirose, T .; Kurosu and M.S. Iida, Jpn. J. Appl. Phys. 34, 5550 (1995), Reference [10]: F.R. Maier, M .; Riedel, B .; Mantel, J .; Listeinand L. Lee, Phys. Rev .. Lett. 85, 3472 (2002)], but the cause of the energy band bending above the surface could not be clarified here.
[0036]
As shown in FIG. 2, ozone decomposes to produce oxygen free radicals. The surface conductivity is reduced because the hydrogen atoms are chemically absorbed by the oxygen radicals onto the surface and partially displaced. A diamond surface having an oxygen-terminated structure generally exhibits insulating properties, and the sheet resistance increases after ozone treatment. Therefore, it can be said that the diamond surface having the hydrogen-terminated structure partially had the oxygen-terminated structure due to the ozone treatment. The energy band bending of the diamond surface having a partially oxygen-terminated structure is reduced due to the formation of a depletion layer in the holes, as shown in FIG. The ozone treatment changed the carrier concentration of the conductive diamond layer channel from P ⁺ to P.
[0037]
A diamond surface having a hydrogen-terminated structure having a positive surface charge is sensitive to Cl ⁻ ions (see Reference [7] above). However, after the ozone treatment c for 60 minutes (see FIG. 3), the surface state partially became an oxygen-terminated structure and the surface charge became neutral as described above, so that the Cl ⁻ ions of the liquid electrolyte partially changed. It is not adsorbed on the surface of the diamond having the oxygen-terminated structure. That is, as shown in FIG. 6, the diamond surface partially having an oxygen-terminated structure is insensitive to Cl ⁻ ions.
[0038]
FIG. 6B shows the threshold voltage when V _DS = −0.4 V. The threshold voltage shifts to a more negative value as the carrier concentration decreases. The absolute threshold voltage increases as the time of the ozone treatment increases. Here, since the ion concentration of the electrolyte is high (KCl 10 ⁻² mol / liter), it is considered that the change in the capacitance value of the solution diffusion layer (Guy layer) may be ignored [Reference [11]: R. See Memming, Semiconductor Electrochemistry, Wiley Interscience, New York, 2001, p. 84. ].
[0039]
Therefore, the shift of the threshold voltage depends on the ozone treatment time and the ratio of the oxygen termination structure on the diamond channel surface. The advantages of ozone treatment are that the threshold voltage can be controlled and the surface charge is neutral. Therefore, it is effective as a channel.
[0040]
Oxidation of diamond is different from oxidation of Si. Oxidation of Si continues to produce a SiO ₂ film continuously at the Si | SiO ₂ interface state. On the other hand, oxidation of the diamond surface by the ozone treatment is limited to the surface layer.
[0041]
FIG. 7 is a diagram showing the result of observing the diamond surface by photoelectron spectroscopy (XPS). FIG. 7 (a) is a hydrogen-terminated diamond surface without ozone treatment, and FIG. 7 (b) is a result of photoelectron spectroscopy (XPS) observation of the diamond surface after ozone treatment for 60 minutes. (EV), and the vertical axis indicates the spectrum intensity (relative unit).
[0042]
From this result, it can be seen that oxygen is clearly generated on the diamond surface after the ozone treatment for 60 minutes.
[0043]
The amount of oxygen on the diamond surface increases as the ozone treatment time increases. As described above, if all the surface conductive channels are removed by the ozone treatment, the diamond field effect of the P ⁺ (source) -i (channel) -P ⁺ (drain) structure in the normally-off mode regardless of the gate metal. A transistor can be realized.
[0044]
Next, a description will be given of a p-channel field-effect transistor having a channel on a diamond surface having a mixture of hydrogen termination and amino termination, which is an application example of the present invention to a biosensor.
[0045]
It should be noted that good results could be obtained by using KBr instead of KCl as the electrolyte solution. The characteristic diagram is shown in FIG.
[0046]
8A shows the case of KCl, and FIG. 8B shows the case of KBr. The horizontal axis indicates the molar concentration (M), and the vertical axis indicates the threshold voltage (V).
[0047]
As shown in FIG. 8A, before the ozone treatment of KCl was performed, the threshold voltage was low. However, as a result of performing the ozone treatment for 50 minutes, the threshold voltage could be increased. Also, as shown in FIG. 8B, in the case of KBr, the threshold voltage was low before the ozone treatment b, but as a result of the ozone treatment for 50 minutes a, the threshold voltage is increased. Was completed.
[0048]
Further, an electrolyte solution having a positive ion such as an alkali ion and a negative ion such as a halogen ion other than these may be used.
[0049]
Further, the threshold voltage is not changed within a range of ± 0.1 V with respect to a change in pH1 to pH14 of the liquid electrolyte and a negative ion such as a positive ion such as an alkali ion and a negative ion such as a halogen ion from 10 ⁻¹ to 10 ⁻⁶ mol / liter. I have to.
[0050]
Next, application to a p-channel field-effect transistor having a biosensor function having a hydrogen termination and an amino termination will be described.
[0051]
FIG. 9 is a schematic view of a p-channel field-effect transistor having a hydrogen terminus and an amino terminus according to an embodiment of the present invention, and FIG. 10 is a schematic view showing a state of action of various biological organisms on the amino terminus.
[0052]
In FIG. 9, 11 is an undoped polycrystalline diamond layer, 12 is an oxygen (fluorine) -terminated insulating region, 13 is a hydrogen-terminated region, 14 is a nano-modified region, 15 is a source electrode, 16 is a drain electrode, and 17 is a source electrode. An epoxy resin for covering, 18 is an epoxy resin for covering the drain electrode, 19 is DNA and biomolecules, and 20 is a liquid electrolyte.
[0053]
Here, the liquid electrolyte 20 is used as a gate, a hydrogen-terminated surface is aminated by a mixed plasma of hydrogen and nitrogen, and a p-channel field-effect transistor is used in which a diamond surface in which hydrogen-terminated and amino-terminated are mixed is used as a channel.
[0054]
As shown in FIG. 10A, a divalent carboxylic acid (succinic acid) 22 acts on the diamond surface 21 which has been aminated at a higher density than silicon.
[0055]
In addition, as shown in FIG. 10B, carboxylation is performed on the diamond surface 21 by the peptide bond 23.
[0056]
Further, as shown in FIG. 10 (c), DNA 25 is bonded to the carboxylated one in FIG. 10 (b) by a peptide bond 24 on the diamond surface 21.
[0057]
As described above, the threshold voltage of the p-channel field effect transistor can be changed by the binding of the DNA and the biomolecule 19 to the channel portion, thereby opening the way as a biosensor.
[0058]
It should be noted that the present invention is not limited to the above embodiment, and various modifications are possible based on the spirit of the present invention, and these are not excluded from the scope of the present invention.
[0059]
【The invention's effect】
As described above, according to the present invention, the following effects can be obtained.
[0060]
(1) A field-effect transistor having a surface channel having no ion sensitivity can be manufactured. Based on the field effect transistor, an organic molecule and a biomolecule having a desired sensitivity can be immobilized, and a highly selective ion sensor or biosensor can be manufactured. be able to.
[0061]
(2) For immobilization of biomolecules, not hydrogen-terminated structures but other terminal structures (oxygen-terminated, amino-terminated) are required. There is a way to fix molecules.
[Brief description of the drawings]
FIG. 1 is a schematic view of a field-effect transistor subjected to an ozone (O ₃ ) treatment according to an embodiment of the present invention.
FIG. 2 is a schematic view of a channel portion subjected to an ozone (O ₃ ) treatment according to an embodiment of the present invention.
FIG. 3 is a characteristic diagram of a threshold voltage [V] with respect to a KCl solution concentration [M] as a gate according to the embodiment of the present invention.
4 is a I _DS -V _DS characteristic view of a field effect transistor of an embodiment of the present invention.
FIG. 5 is a diagram illustrating an energy band of diamond having a hydrogen termination structure of a field effect transistor according to an embodiment of the present invention.
FIG. 6 is a diagram showing a state in which a diamond surface partially having an oxygen-terminated structure is responsive to Cl ⁻ ions.
FIG. 7 is a diagram showing a result of observing a diamond surface of a field-effect transistor by photoelectron spectroscopy (XPS).
FIG. 8 is a diagram showing characteristics of a threshold voltage (V) with respect to a molar concentration (M) of an electrolyte solution of a field-effect transistor showing an example of the present invention.
FIG. 9 is a schematic view of a p-channel field-effect transistor having a hydrogen terminus and an amino terminus according to an embodiment of the present invention.
FIG. 10 is a schematic diagram showing the state of action of various biological organisms on the amino terminus of a p-channel field effect transistor according to an embodiment of the present invention.
[Explanation of symbols]
REFERENCE SIGNS LIST 1 high-resistance surface channel 2 ozone (O ₃ ) treatment 3 p-type surface conductive layer 4, 15 source electrode 5, 16 drain electrode 6, 17 epoxy resin covering source electrode 7, epoxy resin covering drain electrode 8 liquid Gate 9 made of KCl as electrolyte Reference electrode (Ag / AgCl)
10, 11 Undoped polycrystalline diamond layer 12 Oxygen (fluorine) -terminated insulating region 13 Hydrogen-terminated region 14 Nano-modified region 19 DNA, biomolecule 20 Liquid electrolyte 21 Diamond surface 22 Divalent carboxylic acid (succinic acid)
23,24 peptide bond 25 DNA

Claims (6)

A p-channel field-effect transistor using a liquid electrolyte as a gate, partially oxidizing a hydrogen-terminated surface by ozone treatment, and using a diamond surface having both hydrogen-terminated and oxygen-terminated as a channel. 2. The p-channel field effect transistor according to claim 1, wherein the threshold voltage can be shifted in a negative direction by increasing the oxygen coverage. 2. The p-channel field effect transistor according to claim 1, wherein a threshold voltage is set for a change in pH1 to pH14 of the liquid electrolyte and a negative ion such as a positive ion such as an alkali ion and a negative ion ^10-1 to ^10-6 mol / liter. Is not changed within a range of ± 0.1 V. A p-channel field effect transistor in which a liquid electrolyte is used as a gate, a hydrogen-terminated surface is aminated by mixed plasma of hydrogen and nitrogen, and a diamond surface having both hydrogen-terminated and amino-terminated channels is used as a channel. 5. The p-channel field-effect transistor according to claim 4, wherein carboxylation is performed by causing a divalent carboxylic acid to act on the amino terminus via a peptide bond. 6. The p-channel field-effect transistor according to claim 5, wherein the amino terminus is carboxylated by a peptide bond, and the DNA is further fixed by a peptide bond.

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